Impact resistant polymer compositions

ABSTRACT

A polypropylene composition having an excellent impact resistance at low temperatures comprising 50-90 percent by weight of crystalline polypropylene, 5-30 percent by weight of polyethylene and 5-40 percent by weight of ethylene/propylene block copolymer having an average molecular weight of not less than 10,000, an ethylene content of 7-93 mol percent and an optional recurring cycle.

United States ?etent Itsuho Aishima Tokyo;

k-llisnya Sakurai, Kawasakl-shi; Atsushl Kitaoka; Yoshihiko Katayama,both 01 Inventors Nobeoka-shi, all of Japan Appl. No. 699,313 Filed Jan.22, 1968 Patented Dec. 14, I971 Assignee Asahi Kasei Kogyo KabushikiKaisha Kita-ku, Osaka, Japan Priority Feb. 2, 1967 Japan 42/6295 IMPACTRESISTANT POLYMER COMPOSITIONS 7 Claims, No Drawings US. Cl 260/876 B,260/878 B, 260/897 A Int. Cl C081 29/12, C08f 15/04 [50] Field 01 Search260/876 B,

Primary Examiner-Murray Tillman Assistant Examiner-H. Roberts Allurney-Robert D. Flynn ABSTRACT: A polypropylene composition having anexcellent impact resistance at low temperatures comprising 50-90 percentby weight of crystalline polypropylene, 5-30 percent by weight ofpolyethylene and 5-40 percent by weight of ethylene/propylene blockcopolymer having an average molecular weight of not less than 10,000, anethylene content of 7-93 mol percent and an optional recurring cycle.

IMPACT RESISTANT POLYMER COMPOSITIONS BACKGROUND OF THE INVENTION 1.Field of the Invention:

This invention relates to an impact resistant composition mainlycomprising crystalline polypropylenez-More particularly, it relates to aternary composition having remarkably improved impact resistance,particularly that at low temperatures, obtained by blending a majorportion of crystalline polypropylene with minor portions of polyethyleneand ethylene/propylene block copolymer.

2. Description of the Prior Art The stereospecific highly crystallinepolypropylene obtained by polymerizing propylene in the presence ofstereospecific polymerization catalysts has a high rigidity and strengthand excellent resistance to high temperature, thus, it is used for themanufacture of shaped articles, films and fibers of various uses inrecent years.

However, one of the fundamental drawbacks of the crystallinepolypropylene is that it is quite brittle at low temperatures, thus, theuse in the field where an impact resistance, particularly that at lowtemperatures, is required has been restricted. Thus, there has beenattempted to improve the impact resistance at low temperatures ofcrystalline polypropylene.

For example, there has been proposed a process in which crystallinepolypropylene is blended with a synthetic rubber as a reinforcing agentto improve the drawback. However, in order to improve the impactresistance at low temperatures of crystalline polypropylene to apractical extent, a considerably large amount of synthetic rubber mustbe blended therewith.

The blending of a large amount of rubber drastically deteriorates theexcellent rigidity, strength and resistance to high temperature, whichare the features of crystalline polypropylene, thus, it isdisadvantageous from the standpoint of the balancing of the physicalproperties.

Another process proposed heretofore is an attempt to improve the impactresistance at low temperatures by blending polyethylene with crystallinepolypropylene. In this process, however, true as it is that there occursno important damage in the superior properties of crystallinepolypropylene such as the rigidity, strength and resistance to hightemperature, as a matter of fact, the impact resistance at lowtemperatures can be improved very little even if a considerable amountof polyethylene is incorporated into the crystalline polypropylene.

There has been proposed still another process for improving the impactresistance of crystalline polypropylene by block copolymerizingpropylene with ethylene to form ethylene/propylene block copolymer.However, the process is by no means advantageous from not only theoperational but also an economical standpoints, since the production ofsuch a copolymer requires critical control and operation and theproduction cost is increased due to the complicated process, in order toobtain practically useful copolymer having improved impact resistance.

SUMMARY OF THE INVENTION We have found, as a result of our concentratedefforts, a novel and useful composition in which the impact resistanceat low temperatures of crystalline polypropylene which has never beenimproved by prior art processes known heretofore is amazingly enhancedwithout deteriorating the rigidity, strength and resistance to hightemperature which are the features of the crystalline polypropylene.

This invention has its basis on an entirely novel finding which cannotpossibly be anticipated by the prior arts known heretofore.

That is, in accordance with this invention, there is provided apolypropylene composition having a remarkably improved impact resistanceat low temperatures comprising a major portion of crystallinepolypropylene and minor portions of polyethylene and ethylene/propyleneblock copolymer having an optional recurring cycle.

One of the features of the composition obtained according to thisinvention is that it has remarkably excellent impact resistance at lowtemperatures.

Another feature of the present composition is that it retains therigidity, strength and resistance to high temperature as high as thoseof crystalline polypropylene, together with the remarkably excellentimpact resistance at low temperatures.

Still another feature of the present composition is that it isinexpensive as compared with ethylene/propylene block copolymer and itaffords shaped articles, fibers, films, etc., having well-balancedphysical properties.

The features of this invention will be explained more practically in thefollowing:

The impact resistance at low temperatures of a binary compositionobtained by blending the same amount of polyethylene as contained in thepresent composition with crystalline polypropylene is not improved atall, and, that of a binary composition obtained by blending the sameamount of ethylene/propylene block copolymer as contained in the presentcomposition with crystalline polypropylene is improved not so much aspractically useful.

In contrast, the ternary composition of this invention is a practicallyuseful composition having well-balanced physical properties including aremarkably excellent impact resistance at low temperatures and arigidity, strength and resistance to high temperature as high as thoseof crystalline polypropylene.

If the same degree of improvement in the impact resistance at lowtemperatures as achieved in the present composition is attempted byethylene/propylene block copolymer alone, the deterioration in therigidity, strength and resistance to high temperature to some extent isalmost inevitable. Whereas, the composition according to this inventionhas a rigidity, strength and resistance to high temperature about ashigh as those of crystalline polypropylene, yet, it has well-balancedphysical properties comparable to those of ethylene/propylene blockcopolymer, and in addition, various useful shaped articles, fibers andfilms can be obtained therefrom easily and inexpensively.

The polypropylene used in practising this invention is a highly specificcrystalline polypropylene having an insoluble portion in boilingn-heptane of not less than percent by weight and a melt flow index of 0.1-100 as measured according to ASTM Dl238-57T at 230 C. with a load of2,l60 g. Such polypropylene having various melt flow indexes may be useddepending upon the purpose of the composition contemplated.

Polyethylene which may be used in the composition of this invention caneither be a high density polyethylene having a density not less than0.93 as measured at 23 C., or, a low density polyethylene having adensity ranging 0.90-0.93 on the same basis as set forth above. However,when a remarkable improvement in the impact resistance at lowtemperatures is particularly desired, the use of a high densitypolyethylene having relatively low melt flow index is preferable.

The ethylene/propylene block copolymer referred to herein designates acopolymer containing monomeric ethylene and propylene as constituentswhich are not distributed in a statistical fashion in a polymeric chain,respectively, but are present blockwise with respect to each other.

More particularly, it designates an ethylene/ propylene block copolymerhaving an average molecular weight of not less than 10,000 and ethylenecontent of 7-93 mol percent, preferably 15-85 mol percent, in which apolymeric molecular chain is formed by homopolymeric ethylene block andhomopolymeric propylene block alone; or, by homopolymeric ethylene orpropylene block and statistical copolymeric blocks of ethylene andpropylene; or, by statistical copolymeric blocks having differentcomposition with respect to monomeric ethylene and propylene in everyindividual block.

In order to obtain the composition of this invention having a remarkablyimproved impact resistance at low temperatures while retaining therigidity, strength and resistance to high temperature about as high asthose of crystalline polypropylene, it is necessary to use 50-90 percentby weight of crystalline polypropylene, 30 percent by weight ofpolyethylene and 5-40 percent by weight of ethylene] propylene blockcopolymer.

In a composition using the ingredients outside the range set forthabove, a good balance between the impact resistance and other mechanicalproperties'such as the tensile modulus, hardness, 'etc., may not beretained and such composition has a poor utility.

1n the blended composition of this invention, a small amount ofconventional thermal and/or light stabilizers may be incorporated intothe composition in accordance with the conventional procedures to takeprecautions not to degrade the qualities of respective constituentpolymers in the mixing or moulding process as well as in the actual useof the composition.

in practicing the present invention, it is important to carry out themixing uniformly in a molten state and a suitable temperature must beselected for an optimum uniform mixing. For this purpose, the mixing bya roll, extruder, Bunbury mixer, or other conventional mixing methodsmay be conveniently adopted.

in the mixing operation for blending crystalline polypropylene,ethylene/propylene block copolymer and polyethylene, these threeingredients may be blended simultaneously altogether, or, two of thesethree ingredients may be first blended followed by blending theremaining ingredient therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples willillustrate this invention more practically. it should not be construed,however, that these examples restrict this invention as they are givenmerely by way of illustration.

in the following examples, percentages referred to therein are percentby weight unless otherwise specifically indicated.

EXAMPLES l-2 Hydrogen-added propylene was polymerized in n-hexane in thepresence of a catalyst comprising titanium trichloride anddiethylaluminum chloride for an hour. At the end of the period, thesupply of propylene was stopped and, after remov- A high densitypolyethylene having a density of 0.95 as measured at 23 C. and anaverage molecular weight of 80,000 and the above-mentioned twoingredients in predetermined proportions were melt kneaded by using aBunbury mixer under a nitrogen atmosphere at 190 C. for 10 minutes Themix thus kneaded was subsequently rolled on an open roll at roomtemperature and the resulting sheet was pelletized at 230 C. under anitrogen atmosphere by using a screw extruder type pelletizer.

The composition thus obtained was compression moulded according to themethod described in ASTM D638-6l to give a test piece of a dumbbellshape. After the test piece was conditioned for 72 hours, the physicalproperties thereof were measured and evaluated according to thefollowing ASTM Standards:

Izod impact strength:

ASTM D25 6-56 unit-kg.cm./cm.

(Notched) Measured at 23 C., 0 C. and 30 C.

Tensile modulus:

(Cross head speed: 0.2 inch/min.)

Rockwell hardness:

AS'I'M D785-5 l unit-R scale Drop-Cone impact strength:

A test piece of 2 mm. thickness was cooled at 20 C. for an hour and acom-shaped weight was dropped thereon from a predetermined height andthe energy required to destroy the sample was measured in terms of k.-m. by using a Falling Missile lmpact Tester made by Toyo Seiki Mfg, Co.

For comparison, the physical properties of the binary compositionsconsisting of crystalline polypropylene and polyethylene; andcrystalline polypropylene and ethylene] propylene block copolymerblended similar to the above-mentioned ternary composition were measuredrespectively. The results are shown in the following table 1:

TABLE 1 Composition (percent) Crystal- Ethylene/ Izod impact strengthDropcorn line propylene kg. cm./cm. impact 'Iensllc Rockwell polypro'Polyblock strength modulus hardness pyleno ethylene copolymer 23 C 0 C.30 C (20 C.) (kg/mm!) (R scale) Comparative examples:

1 100 0 0 2. 6 1. 76 l. 0.07 118 8G 00 10 0 3. 7 1. 1. 70 0. 09 110 7980 20 0 3.8 1.80 1.71 0.12 108 70 70 30 0 3. 8- 1. 1. 80 1. 13 70 00 010 2. 45 1.72 1.70 0.08 111 80 80 0 20 2. 60 1. 74 1, 6i) 0. 08 103 7970 0 30 2. 70 1. 72 l. 70 0. 0!) 102 77 ing the unreacted propylenemonomer under a reduced pressure, there was supplied hydrogen-addedethylene for 20 minutes, then, polymerized for an hour. The continuouspolymerization was carried out by repeating the above-mentionedprocedures.

The resulting copolymer was purified by methanol containing hydrochloricacid and there was obtained a powdered,

crystalline ethylene/propylene block copolymer.

The resulting copolymer had an intrinsic viscosity as measured intetralin at C., hereinafter referred to simply as "intrinsic viscosity",of 3.0 and an insoluble portion in n-hephydrogen-added propylene wasagain" In contrast, the compositions of this invention shown in examplesl and 2 exhibit quite excellent impact resistance and the tensilemodulus and hardness are about as high as those of tane of 95 percent.According to the conventional infrared ab- 75 crystalline polypropylene.

80 percent and an ethylene content of 23 mol percent as determined bythe conventional infrared absorption spectrography obtained according tothe same procedures as described in examples l-2 except that a mixtureof ethylene and The wmary P Obmined g f l propylene was used in place ofthe hydrogen-added ethylene; 81110111118 of 8 7 9 p yp py f 8 an mmnslca crystalline polypropylene having an intrinsic viscosity of 2.0 vllcomyof L5 and msohfble P n'heptane of 96 and an insoluble portion inn-heptane of 96 percent; and a Percent; a P y y having a 0f and anpolyethylene having a density of 0.96 and an average molecuaveragemolecular weight of 50,000; and an l i ht f 100,000. ethylepe/propyleneblock copolymer having an intrinsic For comparison, the binarycomposition of crystalline viscosity of 3.5, an insoluble portion inn-heptane of 96 perpolypropylene d polyethylene and the binarycomposition cent and an ethylene content of 45 mol percent as detenninedf crystalline oly ro ylene and ethylene/propylene block by theconventional infrared spectrography obtained accordcopolymer w btained.ing to the same procedures as described in examples 1-2 ex- The testpieces were prepared according to the same cept that the amount ofhydrogen-added ethylene supplied proceduresasdescribed in examples 1-2and the physical prowas changed. perties thereof were measured andevaluated according to For comparison, the binary composition ofcrystalline ASTM Standards. The results are shown in the following tablepolypropylene and polyethylene and the binary composition TABLE 3Composition (percent) Crystal- Ethylene/ Izod impact strength Drop-cornlino propylene kg. cm. cm. impact Tensile Rockwell polypro- Polylockstrength modulus hardness pylene ethylene copolymer 23 C. 0 C. C. (20C.) (kg/mm!) (R scale) Comparative examples:

100 0 0 2. 4 1. 72 1. 75 0. 07 117 86 so 20 0 3. s 1. 86 1. 70 0. 12 10776 80 0 20 2. 6 1. 74 1. 70 0.08 102 60 80 10 10 7.0 4. 1 2. 9 6.50 10770 80 1s 15 7. 5 4. 2 3. 5 7.00 10s 80 of crystalline polypropylene andethylene/propylene block As shown in the above table 3, the ternarycompositions of copolymer were obtained, respectively. this invention ofexample 5-6 have improved impact re- The test pieces were preparedaccording to the procedures sistances at low temperatures andwell-balanced physical proas described in examples l-2 and the physicalproperties pertiesascompared with the comparative examples 11-13.

thereof were measured and evaluated according to ASTM Standards:

The results are shown in the following table 2.

EXAMPLES 7-8 The ternary compositions and the binary compositions asTABLE 2 Composition (percent) Crystal- Ethylene] Izod impact strengthDrop-corn line propylene g. cm./cm. impact Tensile Rockwell polyproblockstrength modulus hardness pylene ethylene copolymer 23 0. 0 C. -30 C.(20 C.) (kg/mm!) (R scale) Comparative examples:

8-- 100 0 0 2. 1. 70 1. 71 0.07 119 87 9., 70 30 0 3. 7 1. 80 1. 70 0.13 97 68 10.-. 70 0 30 2. 9 1. 75 1. 70 0. 09 102 77 Examples:

As can be noted from the above table 2, the ternary compositions of thisinvention shown in examples, 3-4 have higher impact strength at lowtemperatures and good balancing of physical properties as compared withthe comparative examples 8-10.

EXAMPLES 5-6 The ternary compositions were obtained by using variousamounts of an ethylene/propylene block copolymer having an intrinsicviscosity of 2.4, an insoluble portion in n-heptane of comparativeexamples were obtained by using various amounts of crystallinepolypropylene and polypropylene and polyethylene as used in examples1-2, and an ethylene/propylene block copolymer having an intrinsicviscosity of 3.1, an insoluble portion in n-heptane of 80 percent and anethylene content of 52 mol percent as determined by the conventionalinfrared absorption spectrography obtained according to the sameprocedures as described in examples 1-2 except that a mixture ofethylene and propylene was supplied in place of hydrogen-addedpropylene.

The physical properties of these compositions were mea sured andevaluated as in the preceding examples. The results are shown in thefollowing table 4:

TABLE 4 Composition (percent) Crystal- Ethylene/ Izod impact strengthDrop-corn line prop lene kg. cmJcm. impact Tensile Rockwell polypro-Polylock strength modulus hardness pylene ethylene copolymer 23 C. 0 C.30 C. (-20 C.) (kg/mm!) (R scale) Comparative example:

14 80 0 20 3. 9 2.1 1.78 0.11 106 Examples:

As shown in the above table 4, the compositions of this invention havean excellent impact resistance and well-balanced physical properties.

sistance comprising:

a. from about 50 to about 90 percent by weight of a crystallinepolypropylene having an insoluble portion in boiling n-heptane of notless than 90 percent by weight and a melt flow index of from about 0.1to about 100 as measured according to ASTM Dl238-57T at 230 C. with aload of2,l60 g.;

b. from about to about 30 percent by weight of a polyethylene having anaverage molecular weight of at least about 50,000; and c. from about 5to about 40 percent by weight of a crystal line ethylene propylene blockcopolymer having an average molecular weight of at least about 10,000,an ethylene content of from about 7 to about 93 mol percent, at leastabout 80 percent thereof being insoluble in n-heptane, and beingselected from the group consisting of l. homopolymeric ethylene blocksand homopolymeric propylene blocks;

2. homopolymeric ethylene blocks and random copolymeric blocks ofethylene and propylene; and

3. homopolymeric propylene blocks and random copolymeric blocks ofethylene and propylene.

2. A composition of claim 1, wherein the polyethylene of (b) has adensity of not less than 0.93, as measured at 23 C.

3. A composition of claim 1, wherein the polyethylene of (b) has adensity of from 0.90 to 0.93, as measured at 23 C.

4. A composition of claim 1, wherein the polyethylene of (b) has anaverage molecular weight of from about 50,000 to about 23 5. Acomposition of claim 1, wherein the ethylene content is from about 15 toabout mol percent 6. A composition of claim 1, wherein the copolymer of(c) has an insolubility in n-heptane of from about 80 percent to about96 percent.

7. A composition of claim 1, wherein the copolymer of (c) has anintrinsic viscosity of from 2.4 to 3.5 in tetralin at i i I

2. A composition of claim 1, wherein the polyethylene of (b) has adensity of not less than 0.93, as measured at 23* C.
 2. homopolymericethylene blocks and random copolymeric blocks of ethylene and propylene;and
 3. homopolymeric propylene blocks and random copolymeric blocks ofethylene and propylene.
 3. A composition of claim 1, wherein thepolyethylene of (b) has a density of from 0.90 to 0.93, as measured at23* C.
 4. A composition of claim 1, wherein the polyethylene of (b) hasan average molecular weight of from about 50,000 to about 100,
 000. 5. Acomposition of claim 1, wherein the ethylene content is from about 15 toabout 85 mol percent.
 6. A composition of claim 1, wherein the copolymerof (c) has an insolubility in n-heptane of from about 80 percent toabout 96 percent.
 7. A composition of claim 1, wherein the copolymer of(c) has an intrinsic viscosity of from 2.4 to 3.5 in tetralin at 135* C.